As shown in FIG. 12 for example, as a conventional gas turbine combustor 1, there is one having a structure in which a pilot burner 3 is arranged at the center position of a combustor main body 2 formed in a cylindrical shape, and a plurality of (for example, eight) main burners 10 are arranged at a uniform pitch in the circumferential direction so as to surround the periphery of the pilot burner 3.
The pilot burner 3 is provided with a pilot nozzle 4 and a pilot air channel 5 formed around the pilot nozzle 4. Pilot fuel supplied through the pilot nozzle 4 is combusted with pilot air supplied from the pilot air channel 5 and forms a pilot flame extending towards the rear side of a flame stabilizer 9. Note that, in the figure, reference numeral 6 is a pilot swirler that is disposed inside the pilot air channel 5 to form a swirling flow, and 7 is a pilot cone formed by expanding the diameter of the downstream end portion of a cylindrical member 8 forming the pilot air channel 5.
The main burner 10 is provided with a main nozzle 11 and a main air channel 12 that is formed at the periphery of the main nozzle 11. Main fuel supplied from the main nozzle 11 is premixed with main air supplied through the main air channel 12 to form premixed gas. This premixed gas is combusted downstream of the flame stabilizer 9 by ignition from the pilot flame. Note that, reference numeral 13 in the figure is a main swirler disposed in the main air channel 12, and it facilitates the premixing with the main fuel by causing the main air to form a swirling flow.
More specifically, in order to prevent or suppress combustion oscillation of about 30 to 80 Hz, which is governed by the flame stability, the above-described gas turbine combustor 1 forms a stable pilot flame (diffusion flame) by the diffusion combustion of the pilot burner 3 and is configured so as to stabilize the premixed flame obtained by combusting the premixed gas by means of ignition whereby this pilot flame bridges to the premixed gas of the main burner 10.
As a conventional technique for preventing combustion oscillation of gas turbine combustors, it has been proposed to extend the flame inside a combustion chamber by having different angles of two or more swirlers provided at the air inlet of premixing ducts. According to this conventional technique, it has been stated that since the generation of heat is spread by extending the flame length, the oscillating force would become smaller (for example, see Patent Citation 1).
Further, a gas turbine combustor has been proposed in which, in order to improve the ignition performance of the premixed gas in a premixed combustion region, air injecting means for injecting air towards the downstream side of a tip portion of a pilot cone is provided, and fuel injecting means for injecting fuel in a flame-stabilizing low speed region, or in the vicinity thereof, formed at the downstream side of a tip portion of a pilot cone is provided on the pilot cone (for example, see Patent Citation 2).
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2003-139326
Patent Citation 2: Japanese Unexamined Patent Application, Publication No. 2005-114193